Electronic and magnetic properties of iridium ilmenites $A$IrO$_3$ ($A=$ Mg, Zn, and Mn)

Abstract

We theoretically investigate the electronic band structures and magnetic properties of ilmenites with edge-sharing IrO6 honeycomb layers, AIrO3 with A = Mg, Zn, and Mn, in comparison with a collinear antiferromagnet MnTiO3. The compounds with A = Mg and Zn were recently reported in Y. Haraguchi et al., Phys. Rev. Materials 2, 054411 (2018), while MnIrO3 has not been synthesized yet but the honeycomb stacking structure was elaborated in a superlattice with MnTiO3 in K. Miura et al., Commun. Mater. 1, 55 (2020). We find that, in contrast to MnTiO3, where an energy gap opens in the Ti 3d bands by antiferromagnetic ordering of the high-spin S = 5/2 moments, MgIrO3 and ZnIrO3 have a gap in the Ir 5d bands under the influence of both spin-orbit coupling and electron correlation. Their electronic structures are similar to those in the spin-orbit coupled Mott insulators with the j eff = 1/2 pseudospin degree of freedom, as found in monoclinic A2IrO3 with A = Na and Li which have been studied as candidates for the Kitaev spin liquid. Indeed, we find that the effective exchange interactions between the j eff = 1/2 pseudospins are dominated by the Kitaev-type bond-dependent interaction and the symmetric off-diagonal interactions. On the other hand, for MnIrO3, we show that the local lattice structure is largely deformed, and both Mn 3d and Ir 5d bands appear near the Fermi level in a complicated manner, which makes the electronic and magnetic properties qualitatively different from MgIrO3 and ZnIrO3. Our results indicate that the IrO6 honeycomb network in the ilmenites AIrO3 with A = Mg and Zn would offer a good platform for exotic magnetism by the spin-orbital entangled moments like the Kitaev spin liquid.